The present invention relates generally to improvements in locking devices and methods and, more particularly, but not by way of limitation, to systems for locking the bonnet of a valve to the body of the valve.
In a common method of valve construction, the body of the valve through which a flow passage is formed, is provided with a threaded well that intersects the surface of the valve and extends into the valve body to cross the flow passage. A bonnet, having a threaded end portion, screws into the well, for a portion of the depth of the well, to form a valve chamber within the body of the valve. In general, the well will be disposed between two opposing sides of the valve and the bonnet will have a plurality of angularly related facets formed on the surface thereof parallel to the screw axis of the bonnet into the valve body, these features providing a means for gripping the bonnet and valve body for screwing the bonnet into the valve body. This mode of valve construction facilitates assembly and repair of the valve in that operating parts of the valve, such parts being disposed within the valve chamber or mounted on the bonnet, are readily accessible when the bonnet is removed from the valve body.
While the above described construction of a valve thus simplifies the manufacture and, should it become necessary, the repair of the valve, it can also give rise to problems. In general, a valve which has been constructed in this manner is opened and closed by turning a valve stem that passes through the bonnet so that, with repeated operation of the valve, the bonnet can work loose in the valve body with the result that the valve will leak. Even worse, the valve stem can become jammed to the bonnet; for example, by the build-up of scale in the valve, so that an inattentive person attempting to open the valve to its maximum flow capacity, might remove the bonnet from the valve.
Because of these problems, bonnet locks have been provided to lock the bonnet into position on the valve body after assembly of the valve. Thus, for example, it is known to form a hole in the valve body at a position that will be adjacent a facet of the bonnet after the valve has been assembled and drive a pin into the hole following the assembly. The pin is fixed to the valve body and engages the facet on the bonnet so that the bonnet is locked into place on the valve body. While pin locking of the bonnet will provide a satisfactory solution to the problems noted above in many circumstances, such mode of locking the bonnet to the valve body can place undesirable limitations on valve manufacture and repair. For example, pin locking depends upon the hole in the valve body being positioned to align with a facet on the bonnet, a condition that is not always consistent with such desirable manufacturing and repair factors as interchangeability of parts and relatively low machining tolerances for such parts. Also, of course, the pin can be difficult to remove, because of its tight engagement with the bonnet, to make it difficult to remove the bonnet for repair purposes.